Moisture-induced short circuits on circuit boards in electrical heat gun accessories are a common fault. Repairing them requires a combination of cleaning, drying, component testing and replacement, while adhering to proper operating procedures to avoid secondary damage. The following analysis covers the causes of the fault, the repair process, the use of key tools, and preventative measures.
When a circuit board gets damp, water molecules adhere to component leads, solder joints, and the surface of the circuitry, forming conductive paths and causing short circuits or parameter drift. This is especially true for circuit boards in electrical heat gun accessories with dense packages such as SOP and SSOP, where the pin spacing is small, making them prone to leakage between adjacent pins and even component burnout. Furthermore, prolonged moisture can cause oxidation of metal components, leading to poor contact or open circuits, further exacerbating the fault.
The first step in repair is to thoroughly clean the circuit board. Spray the surface with alcohol or a dedicated circuit board cleaner, and gently brush the solder joints and component leads with a soft brush to remove oxides and dirt. Care should be taken to avoid liquid seeping into the components, especially under BGA-packaged chips. After cleaning, use compressed air or a hairdryer (on a low setting) to dry the surface to prevent residual moisture from causing secondary short circuits.
Drying is a crucial step. Place the circuit board in a drying oven at a temperature not exceeding 60℃ for approximately one hour to ensure complete evaporation of moisture. If drying equipment is unavailable, allow it to air dry naturally in a dry, well-ventilated area, but this should be extended to at least 24 hours, with periodic turning to ensure even drying. Avoid high-temperature baking to prevent component cracking or solder joint detachment due to thermal expansion and contraction.
Component testing and replacement require meticulous operation. Use a multimeter to test the parameters of components such as capacitors and resistors, paying particular attention to electrolytic capacitors and surface-mount components that are easily damaged by moisture. If bulging, leakage, or abnormal parameters are found in components, use a hot air gun to heat the solder joints, remove the damaged component, and clean any residual solder from the pads. When replacing with new components, control the hot air gun temperature between 300-350℃, heating the pads evenly to avoid localized overheating that could deform the circuit board.
The hot air gun can be both a source of fault and a useful repair tool in the repair process. If the circuit board becomes damp due to improper use of the hot air gun (e.g., excessively high temperature, too close blowing distance), first check the equipment's sealing, and replace any worn nozzles or heating elements. During repair, a low-temperature setting on the hot air gun can be used to assist drying, but it must be kept at least 5cm away from the circuit board, and the nozzle should be continuously moved to prevent localized overheating.
The soldering process directly affects the repair quality. After replacing components, use the hot air gun to evenly heat the solder pads. Once the solder melts, quickly place the component and adjust its position to ensure pin alignment. Avoid moving components before cooling to prevent cold solder joints. After soldering, use a magnifying glass to check if the solder joints are full and free of bridging; resolder if necessary.
Preventative measures can reduce the risk of subsequent failures. When using electrical heat gun accessories in humid environments, use a moisture-proof cover or store them in a sealed box with desiccant. Regularly check the condition of the circuit board, especially before the rainy season, and perform a thorough drying process. Furthermore, choosing circuit boards with a three-proof coating (moisture-proof, salt spray-proof, and mildew-proof) can significantly improve moisture resistance.
